The design of the tooth geometry of bevel gears is generally effected symmetrically relative to an axis of symmetry that runs through the gear center and radially through the tooth. This is justified on the basis that toothed gears are generally designed and produced to operate equally in both directions (forward and backward).
Depending on the direction of operation, an individual tooth during the transmission of torque has a load flank that is engaged and transmits the torque to the load flank of the opposing tooth, and a nonworking flank. When the toothed gear rotates, the nonworking flank of a tooth comes into contact either partially or not at all with the following opposing tooth of the meshing toothed gear so long as there is no reversal in the direction of rotation.
In practice, bevel gear units often do not require any reversal of the direction of rotation. Nevertheless, the flanks of the individual teeth of a toothed gear are produced identically and further machined for both rotational directions.
There are a variety of approaches for increasing the maximum possible transmission of force for a gear. One approach is to have the surface undergo heat treatment in order to prevent damage to the tooth flanks. Damage to tooth flanks occurs, for example, in response to excessively high contact pressures. To avoid this, manufacture of the tooth geometry is, among other approaches, followed by finishing the surface, i.e. subjecting it to surface treatment or hardening it. In other approaches, the tooth shape is optimized and its basic rack profile is standardized by DIN 867.